This relates generally to integrated circuits, and more particularly, to integrated circuits with inductors.
Integrated circuits often include circuitry such as wireless communications circuitry that uses inductors. Inductor-based wireless communications circuitry typically includes a resonant circuit that is formed by an inductor and capacitors connected in parallel. This type of resonant circuit is sometimes referred to as an LC “tank.”
An LC tank can be characterized by a tank quality factor Q, which is a dimensionless metric that describes the bandwidth of the resonant circuit relative to its center frequency. The tank Q may be defined as the ratio of the powered stored in the resonant circuit to the power dissipated by the resonant circuit via resistance and reactance. As a result, a higher tank Q typically indicates a lower rate of energy loss relative to the stored energy in the tank and a better frequency selectivity of the band-pass filter, whereas a lower tank Q indicates a higher rate of energy loss and worse frequency selectivity.
It is generally desirable to form LC tanks that exhibit higher Q factors. In conventional integrated circuits, inductor structures and capacitor structures are typically formed over a p-type silicon substrate. During operation of the LC tank, the inductor may apply an AC electric field to the p-type silicon substrate, which may induce undesired current flow in the silicon substrate (i.e., the LC tank may suffer from energy loss due to parasitic capacitive coupling to the silicon substrate). This effect is exacerbated at high frequencies of operation such as in the 10 GHz range and beyond for an on-chip inductor in the LC tank. Loss incurred in this way can result in an undesirable amount of power being consumed and a degradation of the frequency selectivity.
It is within this context that the embodiments described herein arise.